Oscillation circuit



April 28, 1931; w KUMMERER 1,802,767

OSCILLATION CIRCUIT Filed Aug. 18 1925 INVENTOR Wm M KUMMERER BY MM AORNEY Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE WILHELMKUMMERER, OF BERLIN, GER-MANY, ASSIGNOR TO RADIO CORPORATION OF AMERICA,A CORPORATION OF DELAWARE OSCILLATION CIRCUIT Application filed August18, 1925, Serial No. 50,983, and in Germany October 1, 1924.

The present invention relates to an arrangement for use in a circuit forthe variation of the wave length of tube transmitters which work upon aclosed oscillation circuit.

a This case arises, for instance, in controlling (modulator)transmitters for separately excited tube transmitters. In such a case acoinrar ely large wave range is usually required and in the majority ofknown arrangements, it has been necessary for the anode coupling to becorrespondingly altered.

The pr sent invention has for its object the provision of a circuit inwhich the proper anode coupling for the oscillation tube is alwaysautomatically preserved.

For a further description of the invention, reference to theaccompanying drawings will be made, in which Fig. 1 shows a fundamentaldiagram of connections as embodied in this invention.

Fig. 2 shows a fundamental diagram of connections as embodied in thisinvention having in addition a variable resistance.

Fig. 3 shows a fundamental diagram of connections as embodied in thisinvention having an additional resistance inserted in parallel with aninductance.

Fig. lrepresents a modification of my invention wherein a resistancelamp is substituted for the variable resistance of Fig. 3, for example,although the application of the lamp is applicable to any of the otherfigures of the drawing.

Referring to Fig. 1, a is theroscillation ube, b is a coil or" variableself inductance variometer), c is a condenser of variable rapacity, (Z,an anode blocking condenser intended to shut oil the direct current, 6,an anode choking coil which is designed to prevent a short circuit byway of the direct current source 7". Coil b jointly with the condenserconstitute the oscillation circuit which, as is well known, offers animpedance of high ohmic resista cc for the frequency to which it hasbeen tuned. With close approximation the resultant virtual resistance ofthe impedance circuit when tuned can be expressed the. followingequation:

where R- represents the total ohmic resistance of the circuit in termsof ohms, L and G represent the self-inductance and capacitance,respectively, in terms othenries and tar-ads, respectively. The value ofZ at which a definite type of tube .is made to operate properly, isconstant within wide limits on varying the wave length. The ohmic resistance of the circuit (damping resistance), however, as a general rulevaries with the wave length in this sense that the resistance of thecoils grows steadily and continuously as the length of the wavedecreases; more particularly speaking, below a certain wave length thehigh frequency resistance of the coil grows markedly. Now, according tothe present invention, by the aid of a convenient mechanical driveindicated generally by the letter h, the condenser with coil b in such apositive manner that the relationship between L and C remains always thesame with reference to the resistance R of the oscillation circuit. Forinstance, if the ohmic resistance of the oscillation circuit wereconstant, then upon the wave length being increased, L and C would haveto be increased in like proportion with the consequence that also theratio LzC is preserved. However, since this presupposition is notfulfilled in most cases, one has to proceed in such a way that thedamping resistance of the circuit is predetermined either by actualmeasurement or else by calculation, the drive being thereupon sodetermined and fixed that the ratio L G changes in the same manner asthe ohmic resistance R.

However, in the practical performance of the idea it may happen that,especially within the range of short waves, the resistance variation ofthe coils with the wave length becomes so pronounced that unfavorableratios L:C or undesirable currents in the oscillation circuit may arise.Another desirable point is to make the mechanical gearing or drivebetween the coil and the con- 0 is to be united" denser as simple indesign as possible but in so doing certain restrictions may be imposedas regards the adjustment of the ratio L1G. Now, in order that thetransmitter may be properly coupled in spite of this situation, avariable ohmic resistance, as shown in Fig. 2 is also inserted in thecircuit before referred to, the said ohmic resistance 9 being actuatedconjointlv with the setting or variation of L and C, The said resistance9 having, for instance, the rotary form, is mounted upon the axis orspindle ofthe rotary condenser, and the same is to be so.

connected that upon the capacitance being decreased, in other Words, inthe, presence ofdecreasing wave-length, the said resistance is graduallycut out whereby the. increase in the total resistance is reducible inany desired extent.

Another form of construction of the said variable resistance consists inthat an un- Yariable ohmic resistance is inserted in the circuit towhich a condenser is connected in parallel as; shown in Fig. 3, the sizeof this condenser being so calculated and chosen that in the presence oflong waves, the capacitive reactance is high comparatively with theohmic resistance, so that the major part of the oscillation-circuitcurrent is caused to flow across the virtual resistance, whereas atshort Waves the condenser constitutes a bridge tree from loss for thevirtual resistance.

Another embodiment of the same idea consists in that an ohmic resistancein the circuit characterized by a marked positive temperaturecoefficient is inserted. For this purpose there could be used, forinstance, a metaLfilament glow-lamp of suitable amperage and voltage theresistance of which, as is well-known changes at the ratio of 1: 10. Ifthe circuit resistance at short waves is very high andthe currentflowing in the circuit low as a consequence, the lamp is caused to burnrather dull and dark, or does not burn at all, and its resistance is butlow. If, then,theresistance of the circuit decreases while the currentgrows, it follows that the resistance of the lamp increases also inproportion as the filament ten'rperature rises.

Having thus described. my invention, what I claim is In a tubetransmitter, the method of maintaining alternating current potential ofa proper amount for the anode coupling for varying conditions of wavelength which consists in varying the inductance and capacitance of the,circuit simultaneously in a fixed ratio, and: simultaneously insertingor cutting-out resistance from the circuit including the, inductance andcapacity at such a rate that a fixed ratio of the inductance to theproduct of capacitance and resistance of the circuit is maintained atall times.

lVILHELM KUMMERER.

